u see chinese communist too up liao. NK only pay lip service to the chinese, if the chinese set too many conditions to it aids to NK, NK would rather NK citizens starve than accepts conditions that were unacceptable to the NK. u think the chinese like the idea of a nuclear power NK who even the chinese have no idea who calling the shots in NK. A nuclear tip missile may only take less than 1 hour to fly to beijing (i no idea of NK missile speed), not something the chinese politburo keen to live under.
chinese always perviced that they were being surrounded by enemies, either the russian or the american. The fact it entire northern border with russia is heavily militarised. and the south have a billion kelings on the other side so PRC like to use burma and pakistan to counter india. Then when vietnam follow the russian line of communism, the chinese throw its weight to the khmer rouge. The chinese have been supplying small arms to the khmer rouge to support khmer rouge claim to the mekong delta which of course result in the counter invasion of the cambodia by vietnam. likewise, the chinese would rather give a token supply of grain and fuel to prop up the NK regime than have american troops and its allies across yalu jiang.
by the way, trade between the two nations not exactly smooth, there are claims of both sides trying to cheat the other on the border towns. even normal citizens of both side of the borders dont trust each other. pop over to dandong to see for yourself, u be surprise to see both side not exactly the "brothers" the media protray them to be.